Tomas Ögren wrote:
On 05 January, 2007 - Mark Maybee sent me these 1,5K bytes:
So it looks like this data does not include ::kmastat info from *after*
you reset arc_reduce_dnlc_percent. Can I get that?
Yeah, attached. (although about 18 hours after the others)
Excellent, this confirms #3 below.
What I suspect is happening:
1 with your large ncsize, you eventually ran the machine out
of memory because (currently) the arc is not accounting for
the space consumed by "auxiliary" caches (dnode_t, etc.).
2 the arc could not reduce at this point since almost all of
its memory was tied up by the dnlc refs.
3 when you eventually allowed the arc to reduce the dnlc size,
it managed to free up some space, but much of this did not
"appear" because it was tied up in slabs in the auxiliary
caches (fragmentation).
We are working on a fix for number 1 above.
Great!
You should *not* be setting arc_reduce_dnlc_percent to zero, even if
you want a large number of dnlc entries. You are tying the arc hands
here, so it has no ability to reduce its size.
Number 3 is the most difficult issue. We are looking into that at the
moment as well.
Any idea where all the memory is going? I sure hope that 500k dnlc
entries (+dnode_t's etc belonging to that) isn't using up about 2GB
ram..?
Actually, thats pretty much what is happening:
500k dnlc => 170MB in the vnodes (vn_cache)
+ 320MB in znode_phys data (zio_buf_512)
+ 382MB in dnode_phys data (zio_buf_16384)
+ 208MB in dmu bufs (dmu_buf_impl_t)
+ 400MB in dnodes (dnode_t)
+ 120MB in znodes (zfs_znode_cache)
---------
total 1600MB
These numbers come from the last ::kmastat you ran before reducing the
DNLC size. Note below that much of this space is still consumed by
these caches, even after the DNLC has dropped it references. This is
largely due to fragmentation in the caches.
/Tomas
------------------------------------------------------------------------
cache buf buf buf memory alloc alloc
name size in use total in use succeed fail
------------------------- ------ ------ ------ --------- --------- -----
vn_cache 240 405388 657696 173801472 948191 0
...
zio_buf_512 512 137801 294975 161095680 43660052 0
...
zio_buf_16384 16384 6692 6697 109723648 5877279 0
...
dmu_buf_impl_t 328 145260 622392 212443136 65461261 0
dnode_t 640 137799 512508 349872128 37995548 0
...
zfs_znode_cache 200 137763 568040 116334592 35683478 0
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